A vehicular apparatus mounted to a vehicle is required to be developed in a short time in view of rapid progress of a portable information terminal, which is connected to the vehicular apparatus by a short range communication such as Bluetooth (registered trademark) and the like. Under this circumstance, it is conceived that a first control means dedicated to control of a vehicle system such as navigation and the like and a second control means dedicated to control of an information system such as HMI (Human Machine Interface) and the like are mounted to different boards. In this structure, the first control means is mounted to the first board and the second control means is mounted to the second board, and card-edge connection is made between the first board and the second board, so that the second board can easily be exchanged with respect to the first board and an apparatus function addition (update) can be easily made. Incidentally, a vehicular apparatus for performing speech recognition of speech data uttered by a user is provided (see Patent Literature 1 for example).
The inventors of the present application have recognized the following.
When the first controller and the second controller are mounted to different boards, a conceivable structure is that the first controller performs speech processing on a first speech data not targeted for the speech recognition and the second controller performs speech processing on a second speech data targeted for the speech recognition. In that regard, when a common A/D converter for performing A/D conversion of each of the first speech data and the second speech data is employed in order to reduce the number of parts, a resultant conceivable structure is that the A/D converter is connected to the first controller and the second controller by a signal line compliant with Inter-IC Sound (I2S) standards. In this structure, the first speech data and the second speech data are transmitted via different channels (L channel and R channel) and the I2S speech data outputted from the A/D converter is branched.
However, the structure with the branch of the I2S speech data outputted from the A/D converter involves the following conceivable difficulties. When a switch provided on an upstream side of the first controller in a signal flow direction switches over between a first connection state in which the first speech data is inputted to the first controller and a second connection state in which different speech data other than the first speech data and the second speech data is inputted to the first speech controller, the path of the I2S speech data in the second connection state is cut at the switch but the path of the I2S speech data in the first connection state is extended to the first controller via the switch. That is, a branch pattern (open stub) is extended by a path that connects between the switch and the first controller.
When the branch pattern is extended from the branch point, I2S clock waveform may be rounded. When the I2S clock waveform is rounded in the speech recognition of the second speech data, a bit deviation may occur due to chattering. Accordingly, the second speech data cannot be accurately determined (retrieved) and as a result, the speech recognition cannot be accurately performed.